Copolymers of ethylene with chlorotrifluoroethylene, tetrafluoroethylene or mixtures thereof are well known in the art, in particular for the manufacture of films and protective layers.
In this field, weatherability, stain resistance and transparency are often considered as valuable properties for a protective film; this is particularly true when these protective films are intended to be used as agricultural films, as protective sheeting for photovoltaic cells, as packaging materials and the like.
In all these fields of use, it has been found particularly advantageous to introduce in the polymer matrix suitable compounds which substantially prevent penetration of ultra-violet light, without affecting penetration of visible light.
Nevertheless, transparency and haze of the films are generally affected due to the poor dispersability of these UV blockers in the fluorinated matrix.
JP 2010143948 (TORAY ADVANCED FILMS) Jan. 1, 2010 discloses a transparent film for use notably for PV cells protection, made from a composition based on a fluororesin and a core-shell filler having a ZnO core and a silicon oxide surface layer, having average particle size of 10 to 50 nm. Its example 1 discloses a composition, comprising, as fluororesin, a commercially available ETFE resin, namely AFLON COP88 AXP, and 0.2 part by mass of ZnO particles coated with silicon oxide and having an average particle size equal to 20 nm. No explicit disclosure is provided regarding the heat of fusion of the ETFE resin.
US 2006052486 (FUJITA KENICHI) Sep. 3, 2006 discloses a resin composition comprising an inorganic-type UV absorber, having an average particle size of preferably of 30 nm or less, which may be optionally surface treated, and a thermoplastic transparent resin, which maybe ETFE. No mention is made of the heat of fusion of the ETFE resin to be used.